Pinch flats are caused when you ride into something that causes a sharp impact — a rock, railroad track or edge of a pothole are prime culprits. The impact compresses the tire so much that the tube is pinched between it and edges of the rim.
This causes 2 small holes about half an inch apart on the rim side of the tube. They look like fang marks, so that’s why pinch flats are also known as snakebite flats.
Most pinch flats are caused by a combination of 3 factors: not enough inflation pressure, tires that are too narrow and/or poor riding technique.
The first line of defense is inflating tires to the “sweet spot” — hard enough to avoid pinch flats but not so hard that ride comfort and handling are compromised. As a tire gets harder, it becomes more unyielding when it hits the small bumps that are part of any road surface.
The result is a tire that’s skittish and prone to chattering in turns. Some authorities speculate that this slows you down because the tire is, in effect, bouncing off each bump in the road and momentarily reducing your forward momentum. I’m not qualified to judge if that’s correct, but I like the feel of some “give” in my tires.
Generally, riders up to 190 pounds on smooth roads can safely and comfortably run 90-100 psi in the rear tire and about 80-90 psi in the front. Experiment to find the pressure that works best for you.
Wider tires help protect against pinch flats because they contain more protective air volume. Consider using 700x25C or even 700x28C tires if pinch flatting is a problem. If your fork doesn’t have enough clearance for wider tires, run the widest size you can on the rear and use a narrower size up front.
Recently, riders have adopted lower pressures and wider tires after research, much of it done by Jan Heine at Bicycle Quarterly, showed that speed didn’t change appreciably with widely different tire pressures while comfort increased with both lower pressures and wider tires. Even pro racers have gone from 23mm tires to 25s and even 30mm on some courses. Research also shows that tires with supple casings are faster than those with rigid sidewalls.
New TPU (thermoplastic polyurethane) tubes like the Schwalbe Aerothan and tubes from Tubolito are an entirely different material than latex and butyl. Very expensive and often more than $30 per tube, they’re billed as lighter than latex, yet tougher than butyl. They claim to be harder to puncture and also more resistant to pinch flats. Even so, I’ve personally pinch flatted one of these tubes on a group ride when someone didn’t call out a very large rock in the road and I hit it with my front tire at full speed. The rock was so large that I’m not sure if I can blame any tube in that particular situation.
More and more roadies are switching to road tubeless, including pro cyclists. Tubeless tires use a liquid sealant instead of a tube. With no tube at all inside the tire, there’s nothing to pinch. If your pressure is too low, you can still bottom out and crack your rim or otherwise damage your wheel though.
As for technique, pay attention to the road surface. When you spot a potential tire biter that you’re not going to be able to miss, slow down and think “light.” Bend your elbows and knees, level the pedals, raise your butt off the saddle and let the bike “float” over the hazard. Riding with the right tire width and air pressure will save you most of the time when you hit something unexpectedly.
larry english says
actually the reason wider tires [may] work better is, their rubber is thicker, so it might cushion the tube a little more.
also they may be taller, so there is more room, before the tube gets squashed.
Kerry Irons says
Within a given tire line, wider tires don’t have thicker rubber. They have more rubber, but it is not thicker. Wider tires have more volume and so can better support a given weight and will deflect less at the same application of force. And of course wider tires will be taller. It is quite difficult to make a tire that is oval shaped – wider but not taller – since the air pressure makes a circle, anchored at each side by the rim.
Marc Baskin says
Experts frequently suggests that we buy tires with that are more supple. When you go to buy a tire, How do you tell whether it is supple or not? Is there is some objective measurement of this?
Casing material and tpi count are good indicators. Cotton sidewalls tend to be the most “supple” and also generally the higher the tpi count the more “supple” a tire tends to be.
Tom in MN says
Problem with wanting to run lower pressures for comfort is that you can’t prove a negative. You’ll only know when you do get a pinch flat that your pressure is too low. I am currently using the 15% drop tables baed on 60/40 weight distribution for my tire width. Having a lower front tire pressure than the rear has made my bike feel more balanced.
You didn’t mention that no pinch flats are a major advantage of tubeless tires, but I have not fealt the need to deal with the sealant hassle. I’ve thought about running tubeless tires (as opposed to tubeless ready that require sealant) without sealant. Putting in a tube after getting a flat is no more work than fixing a flat in a tubed tire and there would be no sealant mess. I carry a spare tube already.
Mik Nolin says
I don’t think I understand the difference between tubeless and tubeless ready.
Is there something you have to do differently to avoid sealant?
Brian Nystrom says
True tubeless tires are designed to seal completely when mounted on tubeless rims. They have an inner rubber liner that completely seals the casing. In essence, they have a “tube” of sorts built-in, which is why they’re generally heavier than tubeless-ready tires. They can be used with sealant, but it’s not required.
Tubeless ready tires are designed to be used on tubeless rims, but they do not have the inner liner that seals the casing; they rely on sealant to do that job. You cannot run them tubeless without sealant, as they will leak.
Either type of tire can be used with a tube, if necessary, This is often the case when fixing flats on the road.
Personally, I use sealant in ALL of my tires – including those with tubes – as it eliminates nearly all of the most common flats. It takes a pretty substantial cut for the sealant not to work. I often go an entire season of road and gravel riding without a single flat.
Brian Nystrom says
BTW, I don’t understand why some riders are so “sealant-phobic”. In my experience over the past decade, sealant isn’t much of a hassle at all and I’ve used in road clinchers, road tubulars, and tubeless tires for gravel, mountain and fat bikes. However, there are some things to keep in mind when using it.
– All tubeless valves have removable valve cores, which make injecting sealant easy, but if you’re using it in tubes, make sure that they have removable cores. Many don’t.
– Take the sealant manufacturer’s suggestions for amounts to use with a grain of salt. Remember, they’re in the business of selling sealant. I typically use between 1/3 and 1/2 the recommended amount of sealant. It works just fine and there’s less to deal with if you have to fix a flat. It also weighs less, if that matters to you. Just remember to add sealant more frequently; in my case that means 2-3 times/year vs. once. It’s no big deal.
– I keep my spare tube in an old cotton sock for protection, but it also serves as a rag to clean up sealant, if necessary. I think I may have had to do this once so far.
– I typically carry a 2-ounce bottle of sealant with me, particularly for off-pavement rides. It’s saved the day more than once.